Vapor generating apparatus



March 31, 1970 P. F. SOKOLOWSKI 3,503,373

VAPOR GENERATING APPARATUS Filed Sept. 1, 1966 FIG. 2

I HHHHI l P hI IHP h I I UH INVENTOR Peter E Sokolowski United States Patent 3,503,373 VAPOR GENERATING APPARATUS Peter F. Sokolowski, Lester, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 1, 1966, Ser. No. 576,570 Int. Cl. F22b 1/16, 21/30; F22d /00 US. Cl. 12232 Claims ABSTRACT OF THE DISCLOSURE A vertical vapor generator, having an annular downcomer passageway encompassing a vapor generating space and defined on its outer periphery by the tubular outer shell and on its inner periphery by a tubular wall defining the vapor generating space, is provided with a ring-shaped member to restrict the downward flow of liquid in the downcomer passageway. The ring member is preferably adjustably supported so that the restricting effect may be adjusted as required to overcome hydrodynamic instability of the vapor generator and render it less sensitive to fluctuations in load.

This invention relates to vapor generators, more particularly to vapor generators of the vertical type having an upright shell structure providing a steam generating zone or space in the lower portion, a vapor collecting space in the upper portion and an internal annular downcomer encompassing the steam generating space.

Vapor generators of the above type operate with a body of liquid maintained at a substantially predetermined level in the downcomer and the vapor generating space, and circulation of liquid through the downcomer to the vapor generating space is sustained in operation by the difference in density between the body of liquid in the downcomer and the mixture of vapor and liquid in the vapor generating space.

Such vapor generators are primarily employed to transfer the heat energy from an atomic reactor to the liquid, usually water, to provide pressurized steam for a steam turbine driven electrical generating plant. In such applications, liquid heated in the atomic reactor is directed through a tube bundle disposed in the steam generating space to cause rapid boiling of the water into steam, since large quantities of steam are required by the turbine.

The present trend in vapor generators is toward compactness with greater vapor generation capacity. With increase in vapor generation capacity, more moisture separation capacity must also be provided in the vapor collecting space to insure that moisture entrained in the vapor is substantially removed before the vapor leaves the vapor generator. Hence, a larger portion of the vapor collecting space is occupied by moisture separating devices than heretofore. Such compactness, however, has been found to have adverse effects on the hydrodynamic stability of the vapor generator rendering it extremely sensitive to load. Such instability is displayed inv periodic fluctuations in liquid level, vapor flow rates and vapor pressure.

It is an object of the invention to provide a vapor generator of the above type having improved hydrodynamic stability characteristics.

It is a further object of the invention to provide a vapor generator in which the fluid pressure drop in the downcomer passageway may be varied, as required to increase the operational stability of the vapor generator.

A more specific object is to provide a restricting structure in the downcomer passageway that is readily adjustable to improve the hydrodynamic stability of the generator.

Briefly, in accordance with the invention there is provideei a vertical vapor generator having an annular downcomer passageway encompassing a vapor generating space and defined on its outer periphery by the tubular outer shell and on its inner periphery by a tubular wall defining the vapor generating space.

The shell and wall are formed in a manner to impart a convergence in the downcomer, with respect to direction of flow of liquid in the downcomer, and a ring-shaped restricting member is disposed in the convergent downcomer portion. The ring is dependingly supported by a plurality of threaded support members attached to the upper portion of the vapor generator and adjustably movable in vertical direction to raise or lower the ring member, thereby to modify its flow restricting effect in the downcomer, as required.

The ring member may be provided with an annular array of apertures or passageways, so that in its lowermost position, wherein it may inadvertently abut the walls defining the convergent downcomer portion, fiow is not completely blocked and the pressure drop thereacross attains a maximum predetermined value.

The above and the objects are effected by the invention as will be apparent from the following description and claims taken in connection with the accompanying drawings, forming a part of this application, in which:

FIGURE 1 is a longitudinal sectional view of a vertical vapor generator having the invention incorporated therein, with some portions in elevation;

FIG. 2 is an enlarged fragmentary view of a portion of FIG. 1; and

FIG. 3 is a sectional view taken on line lII-III of FIG. 2.

Referring to the drawing in detail, in FIG. 1 there is shown a vapor generator 10 of the vertical type comprising a vertical by extending tubular outer shell or casing 11 having a vapor generating space 12 in its lower portion, a vapor collection space 13 in its upper portion, a liquid inlet 14 at the side and a vapor outlet 15 at the top.

The vapor generating space 12 is defined by an openended tubular wall structure 17 disposed in a central position and extending in axial direction, and in the space 12 there is provided a bundle of upstanding hairpin tubes 18 having their terminal open-ended portions 19 received in a transversely extending partition 20. The partition 20, usually called a tube sheet, forms the lower wall 21 of the vapor generating space 12 and together with a downwardly extending partition 22 and the lower end portion 24 of the shell forms a pair of chambers 25 and 26. The lower shell portion 24 is provided with a tubular fluid inlet 27 communicating with the chamber 25 and a fluid outlet 28 communicating with the chamber 26.

The tubular wall 17 is of smaller diameter than the internal wall 29 of the outer shell 11 and jointly therewith defines an annular downcomer passageway 31. Also, the lower edge portion of the tubular wall 17 is disposed in spaced relation with the tube sheet surface 21 to provide an annular liquid inlet 33 for the vapor generating space 12.

The tubular wall 17 has an upper open-ended portion 35 of reduced cross-sectional area providing an outlet 36 for the vapor generated in the generating space. Since the vapor is laden with moisture incurred by entrainment of fine particles of liquid during ebullition, a first stage moisture separator (not shown) of any suitable type may be disposed within the end portion 35.

Above the vapor outlet 36 additional moisture separating apparatus 37 of any suitable type may be employed to provide second stage removal of residual moisture from the vapor before it is delivered from the vapor outlet 15 to vapor utilizing equipment such as a vapor turbine (not shown).

Liquid from any suitable supply, for example water from the condenser of the above-mentioned turbine, is admitted through the inlet 14 and thence sprayed in an annular pattern by an annular array of apertures 38 provided in a ring manifold 39 attached to the inner wall 29 in any suitable manner.

As thus far recited, the structure is substantially conventional and operates in the following manner. Liquid is injected by the manifold 39 into the downcomer passageway 31 at a rate to maintain a level LL in the downcomer passageway. The liquid flows downwardly in the downcomer and then into the vapor generating space 12 by way of the annular inlet 33.

Heated liquid from any suitable heating source (for example a nuclear reactor, not shown) is directed into the inlet chamber 25 by wayof the inlet 27 and then flows through the tubes 18 to the outlet chamber 26 and is returned to the heating source by way of the outlet 28.

Accordingly the bundle of tubes 18 is immersed in the body of liquid within the vapor generating space 12 and, in the resulting heat exchange, ebullition occurs with the formation of vapor at a high rate. The vapor flows upwardly through the outlet 36 into the collecting space 13 and then through the moisture separating apparatus 37 to the outlet 15.

During its flow through the upper end portion of the tubular wall 17, some moisture is disentrained from the upwardly flowing vapor and drops by gravity onto the body of liquid LL. As the thus partially demoisturized vapor continues its travel through the moisture separating apparatus 37, additional moisture is disentrained and also drops by gravity onto the body of liquid. Accordingly, the vapor is delivered from the outlet 15 in a substantially dry state to a vapor turbine or other vapor utilizing equipment (not shown).

The vapor generator 10 is susceptible of a wide range of operation, i.e., the steam generation rate may be regulated to suit the demand or load thereon by varying the rate at which liquid is injected by the manifold 39 and/ or the flow rate or temperature of the heating liquid supplied to the bundle of tubes 18. However, the steam generator is very sensitive to operation at high load conditions and may become hydrodynamically unstable, as in dicated by periodic fluctuations in the liquid level, vapor flow rate, and vapor pressure.

In accordance With the invention, to overcome such problems and to improve the generator stability, the upper portion 42 of the downcomer passageway 31 is defined by upwardly divergent surface portions 43 and 44 provided, respectively, on the inner wall structure 17 and the outer shell 11, thereby imparting a frustoconical shape thereto. Accordingly, the upper passageway portion 42 is of considerably wider radial dimension in its upper portion and progressively becomes narrower or converges in downstream direction until it coincides with the radial width of the lower portion of the downcomer passage way 31.

Within the convergent passageway portion 42, there is provided a ring-shaped plate member 45 of smaller transverse width than the average width of the passageway portion 42. In the figures, the plate member 45 is positioned in the median portion of the passageway portion 42 and is disposed in spaced relation with the surface portions 43 and 44.

A plurality of upstanding support rods 46 are attached to the plate member 45 in a peripherally spaced annular array. The rods 46 are provided with threaded terminal portion 47 which extend through openings 48 in a deck' or mounting plate 50 disposed in the upper portion of the shell 11. The mounting plate 50 may be supported-in any suitable manner and'is provided with a plurality of apertures 52 to permit flow of vapor therethrough, as indicated in FIG. 1.

Each of the rods 46 is adjustably supported by a flange member 54 having a nut 55 secured thereto which in turn '4 is secured (againt rotation) to the disk plate 50 by bolts 56.

The range of adjustment of the plate member 45 is from an uppermost position near the top of the convergent passageway to a lower position B-B adjacent the lowermost region of the convergent passageway portion 42. The width of the plate member 45 is so proportioned that in the lowermost position BB the plate may accidently block or extremely resist flow of liquid in the downcomer passageway. To-obviate this possibility and to enhance the damping characteristics of the plate member, a large number of uniformly spaced apertures or passages 57 are provided therein.

During operation, the plate member 45 may be subjected to vibrations. However this possibility is obviated or at least minimized by provision of a cylindrical rib member 58 attached to the lower surface of the plate member and effective to stiffen the plate.

At assembly, the flange and nut members 54, 55 are rotated about the threaded end portion- 47 of the rods until the plate member 45 is positioned to obtain a predetermined liquid pressure dropacross the plate which is required to ensure stable operation of the vapor generator. Then the flange is secured to the disk plate 50 by the bolts 56.

When the vapor generator is tested for performance at installation, the hydrodynamic stability is carefully noted, and, if required, the plate member 45 may be adjusted to a lower position to increase the pressure drop thereacross, or, if indicated, it may be adjusted to a higher position to decrease the pressure drop thereacross.

By way of example, but not by way of limitation a representative maximum pressure drop across the plate member 45 is on the order of about 2-3 p.s.i. (in the lowermost position) while in its uppermost position the pressure drop is practically negligible. In the initially adjusted position the pressure drop is about 11 /z p.s.i. The range of travel (from uppermost position to B-B) may be on the order of about 12 inches but may vary to a greater or lesser degree depending on the length and rate of convergence of the passageway portion 42.

It will now be seen that the invention provides a simple, yet effective, arrangement for regulating the pressure drop characteristics in a vapor generator of the type described by imposing a finely adjustable pressure drop in the downcomer passageway.

While the invention has been shown in one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof.

I claim as my invention:

1. In a vertical vapor generator comprising a tubular outer shell having a vapor generating space in its lower portion; a vapor collecting space in its upper portion; and a vapor outlet communicating v with said collecting portion,

means defining an annular downcomer passageway encompassing said vapor generating space,

means for admitting liquid to be evaporated to said downcomer passageway, and

means providing a communication between the lower portion of said downcomer passageway and said vapor generating space, whereby during operation a substantial level of liquid is maintained in said downcomer passageway to feed said vapor generating space with liquid to be evaporated,

the improvement comprising means disposed in said downcomer passageway for restricting the cross-sectional area of said passageway,

said downcomer passageway being of predetermined cross-sectional area, and

said restricting means being adjustable to vary its restricting effect on the passageway.

2. The structure recited in claim 1, wherein the downcomer passageway has a portion that is convergent in the direction of liquid flow therethrough, and

the restricting means is disposed in said convergent portion and is adjustable by movement in vertical direction.

3. The structure recited in claim 1, wherein the restricting means comprises an annular member encompassing the vapor generating space, and further including means for adjustably positioning annular member.

4. The structure recited in claim 1, wherein the restricting means comprises an annular plate member encompassing the vapor generating space, and

said plate member is provided with an annular array of flow passages 5. The structure recited in claim 2, wherein the restricting means comprises an annular plate member encompassing the vapor generating space, and further including a plurality of vertically extending threaded members for adjustably supporting said plate member.

6. The structure recited in claim 5 and further ineluding means disposed in the vapor collecting space for supporting the adjustable support members,

said support members depending from said support means, and

the annular plate member being provided with an annular array of flow passages.

7. The structure recited in claim 5, wherein the plate member is adjustable from an uppermost position to a lowermost position wherein it substantially blocks flow of liquid thereabout, but is further provided with an annular array of openings to permit flow of liquid therethrough when in the lowermost position. 8. In a vertical vapor generator comprising a tubular outer shell having a vapor generating space in its lower portion; a vapor collecting space in its upper portion; and a vapor outlet communicating with said collecting portion,

means defining an annular downcomer passageway encompassing said vapor generating space,

means for admitting liquid to be evaporated to said downcomer passageway, and

means providing a communication between the lower portion of said downcomer passageway and said vapor generating space, whereby during operation a substantial level of liquid is maintained in said downcomer passageway to feed said vapor generating space with liquid to be evaporated,

the improvement comprising a ring member encompassing said vapor generating space and disposed in said downcomer passageway for restricting the crosssectional area of said passageway.

9. The structure recited in claim 8, wherein said ring member is provided with an annular array of flow passages.

10. The structure recited in claim 8, and further including a. plurality of vertically extending members disposed in said vapor collecting space for supporting said ring member,

References Cited UNITED STATES PATENTS 2,862,479 12/1958 Blaser et a1 122-34 3,103,206 9/1963 Halvorsen et al. 122-34 3,242,909 3/1966 Stern et a1. 122-34 KENNETH W. SPRAGUE, Primary Examiner 

